Reducing rebuild time in a computing storage environment

ABSTRACT

Embodiments for reducing rebuild time in a computing storage environment in by a processor. One or more disk drive failures in a Redundant Array of Independent Disks (RAID)- 6  may be rebuilt by holding at least three parity strips per stripe while using one or more of the at least three parity strips according the one or more disk drive failures.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates in general to computing systems, and moreparticularly to, various embodiments for reducing rebuild time in acomputing storage environment using a computing processor.

Description of the Related Art

Computing systems may be found in the workplace, at home, or at school.Computer systems may include data storage systems, or disk storagesystems, to process and store data. A storage system may include one ormore disk drives, which may be configured in an array, such as aRedundant Array of Independent Disks (RAID) topology. In a RAID system,data is stored redundantly across multiple disks in a variety ofconfigurations to provide data security in the event of a hardware orsoftware failure.

As the technology field grows exponentially each year and ever-growingamounts of critical data are stored on storage systems such as RAIDs,the need to rebuild failed disk drives becomes increasingly paramount.Consequently, the need for advancement in the data storage field is ofgreat precedence.

SUMMARY OF THE INVENTION

Various embodiments for reducing rebuild time in a computing storageenvironment by a processor, are provided. In one embodiment, by way ofexample only, a method for faster rebuild time in a RAID 6 computingstorage environment, again by a processor, is provided. One or more diskdrive failures in a Redundant Array of Independent Disks (RAID)-6 may berebuilt by holding at least three parity strips per stripe and using oneor more of the three parity strips according the one or more disk drivefailures.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a block diagram depicting an exemplary cloud computing nodeaccording to an embodiment of the present invention;

FIG. 2 is an additional block diagram depicting an exemplary cloudcomputing environment according to an embodiment of the presentinvention;

FIG. 3 is an additional block diagram depicting abstraction model layersaccording to an embodiment of the present invention;

FIG. 4 is a block diagram depicting a stripe in Redundant Array ofIndependent Disks (RAID) 6 topology in accordance with aspects of thepresent invention;

FIG. 5 is a block diagram depicting comparing a Redundant Array ofIndependent Disks (RAID) 6 topology to an enhanced Redundant Array ofIndependent Disks (RAID) 6 in accordance with aspects of the presentinvention;

FIG. 6 is a table diagram listing disk failure combinations and rebuildsfor the various disk failure combinations using an enhanced RedundantArray of Independent Disks (RAID) 6 in accordance with aspects of thepresent invention;

FIG. 7 is a table diagram listing a table listing disk failurecombinations and rebuilds for the various disk failure combinationsusing an enhanced Redundant Array of Independent Disks (RAID) 6 inaccordance with aspects of the present invention;

FIG. 8 is an additional flowchart diagram depicting an exemplary methodfor reducing rebuild time in a computing storage environment by aprocessor in which aspects of the present invention may be realized; and

FIG. 9 is an additional flowchart diagram depicting an exemplary methodfor reducing rebuild time in a computing storage environment by aprocessor, again in which aspects of the present invention may berealized.

DETAILED DESCRIPTION OF THE DRAWINGS

A Redundant Array of Independent Disks (“RAID”) is an array, or group,of hard disk drives controlled by a single array controller and combinedto achieve higher transfer rates than a single, large drive. Even thoughmultiple drives are controlled by one adapter, the RAID device appearsas one drive to the data processing system. Depending on theconfiguration, the RAID device will increase the level of protection andstorage capacity for a data processing system over a single, hard diskdrive. The primary functions of the RAID system are to increase theavailability, protection and storage capacity of data for a dataprocessing system.

RAID technology generally distributes data across the drives accordingto the format of the particular RAID classification (RAID 1, 2, 3, 4, 5or 6). Copies or portions of data for a particular file may be writtenin segments on more than one disk drive, a process referred to as“striping.” By storing the data and instructions on multiple drives,higher data transfer rates are enhanced by the ability of the controllerto schedule read and write commands to multiple drives in parallel.

When one disk of the RAID fails, data from that failed disk must beregenerated, e.g., rebuilt using error correction information from theremaining disks in the group. That is, when a disk-drive component of aRAID fails, the RAID may be rebuilt to restore data redundancy. This maybe accomplished by replacing the failed disk-drive component with astandby disk-drive component and copying and/or regenerating the lostdata on the standby disk-drive component. Ideally, the RAID will berebuilt as expeditiously as possible to minimize the possibility thatanother disk-drive component will fail and result in permanent dataloss.

When a RAID is being rebuilt due to a disk failure, the read/writeresponse time are negatively impacted due to the competition forresources. If more resources are dedicated to rebuilding the RAID, theI/O performance suffers. If more resources are dedicated to servicingI/O requests, the rebuild time is extended. The longer rebuild timeincreases the probability that a failure will occur that results inpermanent data loss. Accordingly, reducing rebuild time (e.g., fasterrebuild time) in a computing storage environment, particularly in a RAID6 topology is critically important to improving computing efficiency.

In one embodiment, by way of example only, a method for faster rebuildtime in a Redundant Array of Independent Disks (RAID)-6 computingstorage environment, again by a processor, is provided one or more diskdrive failures in a RAID-6 may be rebuilt by assigning a first paritystrip to a first section of a stripe and a second parity strip to asecond section of the stripe and a third parity strip to the entirestripe and rebuilding the first section or the second section accordingto a defined order based on a location of one or more faileddisk/strips. The first parity strip is a P parity strip, the secondparity strip is a P parity strip, and the third parity strip is a Qparity strip.

It is understood in advance that although this disclosure includes adetailed description on cloud computing, implementation of the teachingsrecited herein are not limited to a cloud computing environment. Rather,embodiments of the present invention are capable of being implemented inconjunction with any other type of computing environment now known orlater developed.

Cloud computing is a model of service delivery for enabling convenient,on-demand network access to a shared pool of configurable computingresources (e.g., networks, network bandwidth, servers, processing,memory, storage, applications, virtual machines, and services) that canbe rapidly provisioned and released with minimal management effort orinteraction with a provider of the service. This cloud model may includeat least five characteristics, at least three service models, and atleast four deployment models.

Characteristics are as follows:

On-demand self-service: a cloud consumer can unilaterally provisioncomputing capabilities, such as server time and network storage, asneeded automatically without requiring human interaction with theservice's provider.

Broad network access: capabilities are available over a network andaccessed through standard mechanisms that promote use by heterogeneousthin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

Resource pooling: the provider's computing resources are pooled to servemultiple consumers using a multi-tenant model, with different physicaland virtual resources dynamically assigned and reassigned according todemand. There is a sense of location independence in that the consumergenerally has no control or knowledge over the exact location of theprovided resources but may be able to specify location at a higher levelof abstraction (e.g., country, state, or datacenter).

Rapid elasticity: capabilities can be rapidly and elasticallyprovisioned, in some cases automatically, to quickly scale out andrapidly released to quickly scale in. To the consumer, the capabilitiesavailable for provisioning often appear to be unlimited and can bepurchased in any quantity at any time.

Measured service: cloud systems automatically control and optimizeresource use by leveraging a metering capability at some level ofabstraction appropriate to the type of service (e.g., storage,processing, bandwidth, and active user accounts). Resource usage can bemonitored, controlled, and reported providing transparency for both theprovider and consumer of the utilized service.

Service Models are as follows:

Software as a Service (SaaS): the capability provided to the consumer isto use the provider's applications running on a cloud infrastructure.The applications are accessible from various client devices through athin client interface such as a web browser (e.g., web-based e-mail).The consumer does not manage or control the underlying cloudinfrastructure including network, servers, operating systems, storage,or even individual application capabilities, with the possible exceptionof limited user-specific application configuration settings.

Platform as a Service (PaaS): the capability provided to the consumer isto deploy onto the cloud infrastructure consumer-created or acquiredapplications created using programming languages and tools supported bythe provider. The consumer does not manage or control the underlyingcloud infrastructure including networks, servers, operating systems, orstorage, but has control over the deployed applications and possiblyapplication hosting environment configurations.

Infrastructure as a Service (IaaS): the capability provided to theconsumer is to provision processing, storage, networks, and otherfundamental computing resources where the consumer is able to deploy andrun arbitrary software, which can include operating systems andapplications. The consumer does not manage or control the underlyingcloud infrastructure but has control over operating systems, storage,deployed applications, and possibly limited control of select networkingcomponents (e.g., host firewalls).

Deployment Models are as follows:

Private cloud: the cloud infrastructure is operated solely for anorganization. It may be managed by the organization or a third party andmay exist on-premises or off-premises.

Community cloud: the cloud infrastructure is shared by severalorganizations and supports a specific community that has shared concerns(e.g., mission, security requirements, policy, and complianceconsiderations). It may be managed by the organizations or a third partyand may exist on-premises or off-premises.

Public cloud: the cloud infrastructure is made available to the generalpublic or a large industry group and is owned by an organization sellingcloud services.

Hybrid cloud: the cloud infrastructure is a composition of two or moreclouds (private, community, or public) that remain unique entities butare bound together by standardized or proprietary technology thatenables data and application portability (e.g., cloud bursting forload-balancing between clouds).

A cloud computing environment is service oriented with a focus onstatelessness, low coupling, modularity, and semantic interoperability.At the heart of cloud computing is an infrastructure comprising anetwork of interconnected nodes.

Referring now to FIG. 1, a schematic of an example of a cloud computingnode is shown. Cloud computing node 10 is only one example of a suitablecloud computing node and is not intended to suggest any limitation as tothe scope of use or functionality of embodiments of the inventiondescribed herein. Regardless, cloud computing node 10 is capable ofbeing implemented and/or performing any of the functionality set forthhereinabove.

In cloud computing node 10 there is a computer system/server 12, whichis operational with numerous other general purpose or special purposecomputing system environments or configurations. Examples of well-knowncomputing systems, environments, and/or configurations that may besuitable for use with computer system/server 12 include, but are notlimited to, personal computer systems, server computer systems, thinclients, thick clients, hand-held or laptop devices, multiprocessorsystems, microprocessor-based systems, set top boxes, programmableconsumer electronics, network PCs, minicomputer systems, mainframecomputer systems, and distributed cloud computing environments thatinclude any of the above systems or devices, and the like.

Computer system/server 12 may be described in the general context ofcomputer system-executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 12 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 1, computer system/server 12 in cloud computing node 10is shown in the form of a general-purpose computing device. Thecomponents of computer system/server 12 may include, but are not limitedto, one or more processors or processing units 16, a system memory 28,and a bus 18 that couples various system components including systemmemory 28 to processor 16.

Bus 18 represents one or more of any of several types of bus structures,including a memory bus or memory controller, a peripheral bus, anaccelerated graphics port, and a processor or local bus using any of avariety of bus architectures. By way of example, and not limitation,such architectures include Industry Standard Architecture (ISA) bus,Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, VideoElectronics Standards Association (VESA) local bus, and PeripheralComponent Interconnects (PCI) bus.

Computer system/server 12 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 12, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 28 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 30 and/or cachememory 32. Computer system/server 12 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 34 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 18 by one or more datamedia interfaces. As will be further depicted and described below,system memory 28 may include at least one program product having a set(e.g., at least one) of program modules that are configured to carry outthe functions of embodiments of the invention.

Program/utility 40, having a set (at least one) of program modules 42,may be stored in system memory 28 by way of example, and not limitation,as well as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. Program modules 42 generally carry out the functions and/ormethodologies of embodiments of the invention as described herein.

Computer system/server 12 may also communicate with one or more externaldevices 14 such as a keyboard, a pointing device, a display 24, etc.;one or more devices that enable a user to interact with computersystem/server 12; and/or any devices (e.g., network card, modem, etc.)that enable computer system/server 12 to communicate with one or moreother computing devices. Such communication can occur via Input/output(I/O) interfaces 22. Still yet, computer system/server 12 cancommunicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 20. As depicted, network adapter 20communicates with the other components of computer system/server 12 viabus 18. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 12. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

Referring now to FIG. 2, illustrative cloud computing environment 50 isdepicted. As shown, cloud computing environment 50 comprises one or morecloud computing nodes 10 with which local computing devices used bycloud consumers, such as, for example, personal digital assistant (PDA)or cellular telephone 54A, desktop computer 54B, laptop computer 54C,and/or automobile computer system 54N may communicate. Nodes 10 maycommunicate with one another. They may be grouped (not shown) physicallyor virtually, in one or more networks, such as Private, Community,Public, or Hybrid clouds as described hereinabove, or a combinationthereof. This allows cloud computing environment 50 to offerinfrastructure, platforms and/or software as services for which a cloudconsumer does not need to maintain resources on a local computingdevice. It is understood that the types of computing devices 54A-N shownin FIG. 2 are intended to be illustrative only and that computing nodes10 and cloud computing environment 50 can communicate with any type ofcomputerized device over any type of network and/or network addressableconnection (e.g., using a web browser).

Referring now to FIG. 3, a set of functional abstraction layers providedby cloud computing environment 50 (FIG. 2) is shown. It should beunderstood in advance that the components, layers, and functions shownin FIG. 3 are intended to be illustrative only and embodiments of theinvention are not limited thereto. As depicted, the following layers andcorresponding functions are provided:

Hardware and software layer 60 includes hardware and softwarecomponents. Examples of hardware components include: mainframes 61; RISC(Reduced Instruction Set Computer) architecture based servers 62;servers 63; blade servers 64; storage devices 65; and networks andnetworking components 66. In some embodiments, software componentsinclude network application server software 67 and database software 68.

Virtualization layer 70 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers71; virtual storage 72; virtual networks 73, including virtual privatenetworks; virtual applications and operating systems 74; and virtualclients 75.

In one example, management layer 80 may provide the functions describedbelow. Resource provisioning 81 provides dynamic procurement ofcomputing resources and other resources that are utilized to performtasks within the cloud computing environment. Metering and Pricing 82provides cost tracking as resources are utilized within the cloudcomputing environment, and billing or invoicing for consumption of theseresources. In one example, these resources may comprise applicationsoftware licenses. Security provides identity verification for cloudconsumers and tasks, as well as protection for data and other resources.User portal 83 provides access to the cloud computing environment forconsumers and system administrators. Service level management 84provides cloud computing resource allocation and management such thatrequired service levels are met. Service Level Agreement (SLA) planningand fulfillment 85 provides pre-arrangement for, and procurement of,cloud computing resources for which a future requirement is anticipatedin accordance with an SLA.

Workloads layer 90 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation 91; software development and lifecycle management 92; virtualclassroom education delivery 93; data analytics processing 94;transaction processing 95; and, in the context of the illustratedembodiments of the present invention, various workloads and functions 96for reducing rebuild time in a RAID 6 computing storage environment suchas, for example, in the hardware and software layer 60. In addition,reducing rebuild time in a RAID 6 computing storage environment such as,for example, in the hardware and software layer 60 may include suchoperations as performance workload analytics, performance profileanalysis, rebuilding one or more disk drives, and other computingstorage related functions. One of ordinary skill in the art willappreciate that the workloads and functions 96 for reducing rebuild timein a RAID 6 computing storage environment may also work in conjunctionwith other portions of the various abstractions layers, such as those inhardware and software 60, virtualization 70, management 80, and otherworkloads 90 (such as data analytics processing 94, for example) toaccomplish the various purposes of the illustrated embodiments of thepresent invention.

It should be noted that in a RAID 5 topology, RAID 5 reads and writesdata segments across multiple data drives and writes parity to the samedata disks. The parity data (“P”) is never stored on the same drive asthe data it protects, allowing for concurrent read and write operations.Within any stripe of a five drive RAID 5 configuration, all drivescontain data information and parity information. If one of the datadrives were to fail, the remaining four data drives and the parity oneach remaining may be used to regenerate user data which improvesimproving data protection.

Alternatively, RAID 6 improves the data protection of RAID 5 byproviding two parity strips (e.g., P parity strip and Q parity strip),as illustrated in FIG. 4. That is, FIG. 4 depicts a RAID 6 topology(with N drives) showing a RAID 6 having 8 strips (e.g., strip 1-6 and Pparity strip and Q parity strip) in a single stripe 410. In one aspect,one or more of the components, modules, services, applications, and/orfunctions described in FIGS. 1-3 may be used in FIG. 4. Also, many ofthe functional blocks may also be considered “modules” of functionality,in the same descriptive sense as has been previously described in FIGS.1-3. Repetitive description of like elements, components, modules,services, applications, and/or functions employed in other embodimentsdescribed herein is omitted for sake of brevity.

As illustrated in block 420, one or more stripes may be included in oneor more disk drives (“drives”) such as, for example, drives A-H. Thatis, both RAID 5 and RAID 6 use striping which means that the data iswritten cyclically over the drives such as, for example, drives A-H, andthe role of each drive is rotated so that strips 1-6, P and Q are spreadover all the drives, as depicted in block 420 depicting a RAID 6topology.

In one aspect, the RAID 6 topology is a scheme of disk redundancy usedto obtain high reliability of a disk array. In a configuration of Ndrives, RAID 6 utilizes 2 drives for parity checking: P parity strip (or“P parity drive”) and Q parity strip (or “Q parity drive”). P parity maybe calculated using an XOR operation and Q may be calculated usingparity and Reed-Solomon codes. Moreover, in one aspect, for dataprotection in RAID 6, RAID 6 includes 2 parity strips and alwaysprotects against 2 failures. P parity and Q parity protect the samestrips/drives. Each stripe has a P parity and a Q parity. A RAID 6device with this configuration, by way of example only, may be depictedas having multiple rows and multiple columns of data drives with eachrow and column ending with a parity drive. Such approaches differ from aRAID 5 that use only a single parity strip.

Thus, the advantage of RAID 6 over RAID 5 is the ability to survive twodisk failures. In this way, a RAID 6 configuration increases thepercentage, storage efficiency, and availability of data (e.g., a99.999% minimum storage system requirement) for a computing storagesystem as compared to RAID 5. However, the disadvantage of RAID 6 is theincreased write overhead and increased capacity overhead.

In one aspect, in selecting a RAID 6 configuration (strip and stripesizes), one or more of the following factors should be considered. 1)The capacity overhead (the P and Q). For example, in RAID 6 there ismore capacity efficient when there are more strips (“N” arbitrarynumber). This also has a direct influence on the drives' endurance. 2)The RAID rebuild time. For example, the more strips there are the moredata must be read to rebuild a failed drive. 3) The number of physicaldrives. For example, the number of strips cannot be greater than thenumber of physical drives. 4) A computer storage system's requiredreliability. For example, in RAID 6 there is no data loss until thereare three simultaneous drive failures. The reliability is a factor ofthe drive's failure rate and the rebuild time. The rebuild time islonger when the drive's capacity is larger and when N is larger (becausethere is more data to read). The probability of data loss is theprobability of a first drive failing, times the probability of two moredrives failing during the rebuild time of the first. The failure rate ofa drive is typically measured using two metrics. The first metric is themean time between failures (“MTBF”) (e.g., failure is per drive). Thesecond metric is the uncorrectable bit error rate (“UBER”) (e.g., afailure is per bit). Thus, there is a built-in tradeoff between capacityoverhead and reliability. Additionally, the rebuild time is a criticalfactor in the reliability of the storage system. The longer a rebuildtakes, the more a computer system is susceptible to data loss.

Accordingly, the present invention provides for an enhanced modificationto RAID 6 that reduces the rebuild time of a single drive failure, aswell as the rebuild time of a double drive failure in manycases/instances. The double drive rebuild time is gained at the expenseof extending the time it takes to fix only the stripes with two failedstrips per stripe. That is, the present invention may hold three paritystrips per stripe, but unlike triple parity RAID, the present inventionuser two parity strips (“Ps”) such as, for example, P1 and P2 where P1is the parity of the first half of the strips and P2 is the parity ofthe second half of the strip. Q may remain as it is defined in RAID 6.In this way the modification is an enhanced RAID 6, where the “enhanced”language indicates an extra P used compared RAID 6.

Turning now to FIG. 5, diagram 500 depicts a comparison of a RAID 6topology 510 to an enhanced RAID 6 (e.g., modified RAID 6 or “RAID 6P)520. As shown, descriptive information is seen relating each of thefunctional blocks 500. In one aspect, one or more of the components,modules, services, applications, and/or functions described in FIGS. 1-4may be used in FIG. 5. Repetitive description of like elements,components, modules, services, applications, and/or functions employedin other embodiments described herein is omitted for sake of brevity.

In one aspect, the present invention provides enhanced RAID 6 (520) byholding three parity strips per stripe. In contrast to triple parityRAID, the present invention provides for only using two parities (“Ps”).In one aspect, a first parity (e.g., “P1,” p-stripe 1 or parity strip 1)may be the parity of a first half of strips in a stripe. A second parity(e.g., “P2,” p-stripe 2 or parity strip 2) may be the parity of a secondhalf of the strips in a stripe. The Q is Reed Solomon over all datastrips as defined in RAID 6. Thus, the enhanced RAID 6 such as, forexample, enhanced RAID 6 (520), the added p indicates the extra P usedcompared RAID 6. Thus, the cost of the enhanced RAID 6 such as, forexample, enhanced RAID 6 (520) may be assumed to be a factor of thenumber of reads required to rebuild a drive.

More specifically in FIG. 5, the upper row is a traditional RAID 6 suchas, for example, RAID 6 (510) where N is 10 and the overhead is equal to20 percent (%) (e.g., 2/10). The lower row is the enhanced RAID 6 suchas, for example, enhanced RAID 6 (520) where N equals 15 with the sameoverhead of 20% (e.g., 3/15). For illustration and comparison, thepresent invention is depicted by intentionally selecting an example forcomparison with equivalent overhead, to compare the rebuild time of theenhanced RAID 6 (520) to that of a non-enhanced RAID 6 (510). The term“p-stripe” is used to indicate a selected portion of the stripe coveredby a single parity (“P”) drive such as, for example, P1 covering a firstsection or first p-stripe in a stripe and/or P2 covering a secondsection or second p-stripe in the stripe. A p-stripe contains (N−1)/2strips, out of which one is P and (N−1)/2−1 are data.

It should be noted that the core structure of the RAID 6 (510) ispreserved in the enhanced RAID 6 (520) since P equals P1 XOR function P2(e.g., P=P1⊕P2), which can be used to carry out any RAID 6 rebuild.Thus, the advantages of the enhanced RAID 6 (520) may include each ofthe following. 1) A single failure in any strip (except Q) is faster torebuild because only one p-stripe must be rebuilt. 2) The chance of adouble failure is reduced because two failures in the same stripe, butseparate p-stripes, are now just a single failure in the enhanced RAID 6(520). A double failure occurs only when there are two failures in thesame p-stripe or there is one error in a p-stripe and an error in Q. 3)The amount of data lost in the event of three drive failures is lowerthan the non-enhanced RAID 6 (510) because data is only lost when thestrips from the same p-stripe are lost, or 2 strips from the samep-stripe and Q.

Using the above example (e.g., N equals 8+2 compared to N equals 12+3),the rebuild time of a single failure in the enhanced RAID 6 (520) isonly 80% of the rebuild time of the non-enhanced RAID 6 (510). It shouldbe noted that even though the examples all discuss the case of 2p-stripes per stripe, the present invention may apply to any number ofp-stripes per stripe. Thus, as illustrated herein, each p-stripe in theenhanced RAID 6 (520) is turned into a RAID 5 configuration. Forexample, the enhanced RAID 6 (520) has a RAID 5 configuration due to P1covering a first section or first p-stripe in a stripe and a second RAID5 configuration due to P2 covering the second section or the secondp-stripe in the stripe, which is further illustrated in the rebuildtable 600.

Turning now to FIG. 6, table 600 depicts lists disk failure combinationsand rebuilds for the various disk failure combinations using an enhancedRAID 6 such as, for example, the enhanced RAID 6 (520) of FIG. 5. In oneaspect, one or more of the components, modules, services, applications,and/or functions described in FIGS. 1-5 may be used in FIG. 6.Repetitive description of like elements, components, modules, services,applications, and/or functions employed in other embodiments describedherein is omitted for sake of brevity.

Specifically, table 600 illustrates a drive failure, corrupted strips,and a rebuild order for the particular failed drive. For example, table600 illustrates a rebuild operation of the enhanced RAID 6 (520)topology. Table 600 depicts every combination of possible drive failuresbeing rebuilt according to a defined order. To further illustrate, thefollowing definitions are used in Table 600. “D{i}” represents a datastrip from p-stripe iϵ{1,2}. Q is the Q parity strip. “DP{i}” is a dataor P parity strip from p-stripe iϵ{1,2}. “P{i}” is a parity of p-stripeiϵ{1,2}. “P” is a parity of a stripe that is equal to the XOR of P1 andP2 (e.g., P is not stored). Thus, table 600 lists all the possiblefailure combinations and specifies the rebuild type for that particulardrive failure. It should be noted that in the table 600, any case thatrefers only p-strip 1 (e.g., D1 and P1) is equally relevant to p-strip2.

For example, for a single drive failure, if the corrupted strip is D1,the rebuild is to rebuild p-strip 1 of RAID 5. Alternatively, if thecorrected strip is P1, the rebuild is to rebuild p-strip 1 of RAID 5.

For two drive failures, if the corrupted strips are DP1 and Q, therebuild is to rebuild P or D's p-strip 1 of RAID 5 and rebuild thestripe for Q in the RAID 6. If the corrupted strips are DP1 (e.g., “DP1”data in parity) and DP2, both p-stripes of RAID 5 are rebuilt. If thecorrupted strips are P1 and D1, the rebuild is to rebuild D1 from otherD's in the stripe and Q and also rebuild P1 from the D's in theparticular P-strip. Alternatively, if there are two corrupted strips(e.g., 2 multiplied by D1), P is calculated by XORing P1 and P2 (e.g.,P1 XOR P2), and the strip is rebuilt using RAID 6 using P, Q, and D's.

For three drive failures, if there are multiple corrupted strips (e.g.,3 multiplied by D1), P-strip 1 is lost. If there are multiple corruptedstrips (e.g., 3 multiplied by D1) or Q and two corrupted strips (e.g., 2multiplied by D1), P-strip 1 is lost or Q may be recalculated based onD2 and potentially re-write P1 for the rebuild. If there are multiplecorrupted strips (e.g., 2 multiplied by DP1 and DP2, p-strip 2 of RAID 5is rebuilt and p-stripe 1 of RAID 6 is rebuilt. If the corrupted filesare Q and DP1 (e.g., anywhere in p-stripe 1) and DP2 (e.g., anywhere inp-stripe 2), the p-stripe 1 of RAID 5 is rebuilt, the p-stripe 2 of RAID5 is rebuilt, and the Q stripe for RAID 2 is rebuilt.

Rebuild Order (Optimal Order of Rebuild)

Thus, due to the striping in a RAID, when a drives fail there will be acombination of the scenarios in Table 600. Table 600 illustrates therebuild times of different RAID configurations. For example, in thenon-enhanced RAID 6 (510), the rebuild operation is to first rebuildstripes with two failures and then repair the stripes with only onefailure. However, as illustrated in table 600, the enhanced RAID 6 520topology depicts there are more combinations. Accordingly, thepreferred/optimal order for enhanced RAID 6 rebuild is as follows. For 3drive failures, Q and one DP in each p-stripe are rebuilt. For 2 drivefailures, 1) Q and one DP are rebuilt (handle the case of loss of q andone DP), and/or 2) DPs from the same p-stripe are rebuilt. For one drivefailure, Q is rebuilt and/or a DP is rebuilt. That is, the rebuild timesof different RAID configurations may be as follows. 1) 3 failures—a) Qand one DP in each p-stripe, and/or b) 2 DPs in one p-stripe and one inthe other. 2) 2 failures—a) Q and one DP, and/or b) 2 DPs from the samep-stripe. 1) 1 failure—a) Q and/or b) DP. It should be noted that the“a)” and the “b)” options are different cases or “states” of a stripe.There may be stripes in all of the above states.

Rebuild Time

It should be noted that in relation to the rebuild time, the comparisonbetween the non-enhanced RAID 6 (510) and the enhanced RAID 6 (520)depends on the size of the RAID stripe. As before, the comparisonbetween the non-enhanced RAID 6 (510) and the enhanced RAID 6 (520) isperformed such that the RAID overhead is equal (e.g., N equals 8+2 fornon-enhanced RAID 6 (510) compared to N equals 12+3 for the enhancedRAID 6 (520)).

Accordingly, for a single failure, the enhanced RAID 6 (520) willrebuild only one p-stripe. This leads to 20% shorter rebuild timecompared to non-enhanced RAID 6 (510) using example above. For a doublefailure, there is a tradeoff. The enhanced RAID 6 (520) has a shortertotal rebuild time when there are many drives, but a longer time whenthere are fewer drives. This is due to the reduced chance of the twofailures residing in the same p-stripe. Additionally, another tradeoffis that the time to rebuild only the stripes with two failures is longerin the enhanced RAID 6 (520). Thus, table 700 of FIG. 7 providesexemplary sample rebuild times for different configuration of theenhanced RAID 6 (520) (where to N equals 12+3) compared to thenon-enhanced RAID 6 (510) (where N equals 8+2).

Amount of Data Lost on Triple Failure

In one aspect, the enhanced RAID 6 (520) loses less data than RAID 6(510) when there is a triple failure because of two reasons. First,unlike the RAID 6 (510), the enhanced RAID 6 (520) stripes do not alwayslose data when there are three failures. Second, when there is a triplefailure, only one p-stripe is lost in the enhanced RAID 6 (520).

Performance

It should be noted that the performance between the enhanced RAID 6(520) (where to N equals 12+3) compared to the non-enhanced RAID 6 (510)(where N equals 8+2) is the same. In one aspect, sequential writes havethe same throughput (for configurations of equal overhead). Also, theInput/output operations per second (“IOPS”) is equal because a randomwrite still requires reading and writing both P and Q.

Turning now to FIG. 8 is an additional flowchart diagram 800 depictingan exemplary method for reducing rebuild time in a computingenvironment, again in which various aspects of the present invention maybe realized. In one aspect, one or more of the components, modules,services, applications, and/or functions described in FIGS. 1-7 may beused in FIG. 8. The functionality 800 may be implemented as a methodexecuted as instructions on a machine, where the instructions areincluded on at least one computer readable medium or one non-transitorymachine-readable storage medium. The functionality 800 may start inblock 802.

One or more disk drive failures in a Redundant Array of IndependentDisks (RAID)-6 may be rebuilt by holding and using at least three paritystrips per stripe while only using two parity strips of the three paritystrips, as in block 804. That is, all 3 parity strips are used but indifferent cases according to the location of one or more corruptedstrips. Also, if there are failures in corrupted strips DP1, DP2 and Q,all three parity strips will be used. The functionality 800 may end, asin block 806.

Turning now to FIG. 9 is an additional flowchart diagram 900 depictingan exemplary method for reducing rebuild time in a computingenvironment, again in which various aspects of the present invention maybe realized. In one aspect, one or more of the components, modules,services, applications, and/or functions described in FIGS. 1-7 may beused in FIG. 9. The functionality 900 may be implemented as a methodexecuted as instructions on a machine, where the instructions areincluded on at least one computer readable medium or one non-transitorymachine-readable storage medium. The functionality 900 may start inblock 902.

A first parity strip of N parity strips (where N may be a positiveinteger or a defined value) may be used/held in a first parity-stripe ofa stripe in a RAID 6 storage system, as in block 904. A second paritystrip of the N parity strips may be used/held in a second parity-stripeof the stripe in the RAM 6 storage system, as in block 906. A thirdparity strip of the N parity strips may be used/held at the end of thestripe in the RAID 6 storage system, as in block 908. One or more diskdrive failures in one or more stripes the RAID 6 storage system may bedetermined/detected, as in block 910. One or more stripes having one ormore disk drive failures and associated with the first parity strip, thesecond parity strip, or a combination thereof may be built according toa defined rebuild order, as in block 912. The functionality 900 may end,as in block 914.

In one aspect, in conjunction with and/or as part of at least one blockof FIGS. 8-9, the operations of methods 800 and/or 900 may include eachof the following. The operations of methods 800 and/or 900 may use/holda first parity strip of the N three parity strips (e.g., at least 3parity strips) in a first parity-stripe of the stripe, use/hold a secondparity strip of the N three parity strips in a second parity-stripe ofthe stripe, and/or use/hold third parity strip of the N three paritystrips at the end of the stripe. The first parity strip is a P paritystrip of the first parity-stripe, the second parity strip is a P paritystrip, and the third parity strip is a Q parity the entire strip.

The operations of methods 800 and/or 900 may rebuild a selected portionof the stripe having a single disk drive failure and associated with afirst parity strip of the N three parity strips, and/or rebuild thestripe having one or more disk drive failures and associated with one ormore of the N three parity strips according to a defined rebuild order.

The operations of methods 800 and/or 900 may rebuild a Q parity strip, adata strip or a single parity strip for a single disk failure uponoccurrence of a single disk drive failure; rebuild a Q parity strip anda data strip or a single parity strip or at least two data strips orparity strips occurring in a similar p-stripe associated with one ormore of the two parity strips upon occurrence of at least two disk drivefailures, and/or rebuild a Q parity strip and a data strip in eachsection of the stripe associated with the two parity strips uponoccurrence of at least three or more disk drive failures.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

1. A method, by a processor, for data recovery in a computing system,comprising: rebuilding one or more disk drive failures in a RedundantArray of Independent Disks (RAID)-6 by holding at least three paritystrips per stripe and using one or more of the least three parity stripsaccording the one or more disk drive failures.
 2. The method of claim 1,further including using a first parity strip of the at least threeparity strips in a first parity-stripe of the stripe, wherein the firstparity strip is a P parity strip of the first parity-stripe.
 3. Themethod of claim 1, further including using a second parity strip of theat least three parity strips in a second parity-stripe of the stripe,wherein the second parity strip is a P parity strip.
 4. The method ofclaim 1, further including using a third parity strip of the at leastthree parity strips at the end of the stripe, wherein the third paritystrip is a Q parity strip.
 5. The method of claim 1, further includingrebuilding a selected portion of the stripe having a single disk drivefailure and associated with a first parity strip of the at least threeparity strips.
 6. The method of claim 1, further including rebuildingthe stripe having one or more disk drive failures and associated withone or more of the two parity strips according to a defined rebuildorder.
 7. The method of claim 1, further including: rebuilding a Qparity strip, a data strip or a single parity strip for a single diskfailure upon occurrence of a single disk drive failure; rebuilding the Qparity strip and the data strip or the single parity strip or at leasttwo data strips or parity strips occurring in a similar p-stripeassociated with one or more of the two parity strips upon occurrence ofat least two disk drive failures; or rebuilding the Q parity strip andthe data strip in each section of the stripe associated with the twoparity strips upon occurrence of at least three or more disk drivefailures.
 8. A system for data recovery in a computing environment,comprising: one or more computers with executable instructions that whenexecuted cause the system to: rebuild one or more disk drive failures ina Redundant Array of Independent Disks (RAID)-6 by holding at leastthree parity strips per stripe and using one or more of the least threeparity strips according the one or more disk drive failures.
 9. Thesystem of claim 8, wherein the executable instructions use a firstparity strip of the at least three parity strips in a firstparity-stripe of the stripe, wherein the first parity strip is a Pparity strip of the first parity-stripe.
 10. The system of claim 8,wherein the executable instructions use a second parity strip of the atleast three parity strips in a second parity-stripe of the stripe,wherein the second parity strip is a P parity strip.
 11. The system ofclaim 8, wherein the executable instructions use a third parity strip ofthe at least three parity strips at the end of the stripe, wherein thethird parity strip is a Q parity strip.
 12. The system of claim 8,wherein the executable instructions rebuild a selected portion of thestripe having a single disk drive failure and associated with a firstparity strip of the at least three parity strips.
 13. The system ofclaim 8, wherein the executable instructions rebuild the stripe havingone or more disk drive failures and associated with one or more of thetwo parity strips according to a defined rebuild order.
 14. The systemof claim 8, wherein the executable instructions: rebuild a Q paritystrip, a data strip or a single parity strip for a single disk failureupon occurrence of a single disk drive failure; rebuild the Q paritystrip and the data strip or the single parity strip or at least two datastrips or parity strips occurring in a similar p-stripe associated withone or more of the two parity strips upon occurrence of at least twodisk drive failures; or rebuild the Q parity strip and the data strip ineach section of the stripe associated with the two parity strips uponoccurrence of at least three or more disk drive failures.
 15. A computerprogram product for, by a processor, data recovery in a computingsystem, the computer program product comprising a non-transitorycomputer-readable storage medium having computer-readable program codeportions stored therein, the computer-readable program code portionscomprising: an executable portion that rebuilds one or more disk drivefailures in a Redundant Array of Independent Disks (RAID)-6 by holdingat least three parity strips per stripe and using one or more of theleast three parity strips according the one or more disk drive failures.16. The computer program product of claim 15, further including anexecutable portion that: uses a first parity strip of the at least threeparity strips in a first parity-stripe of the stripe, wherein the firstparity strip is a P parity strip of the first parity-stripe; or uses asecond parity strip of the at least three parity strips in a secondparity-stripe of the stripe, wherein the second parity strip is a secondP parity strip.
 17. The computer program product of claim 15, furtherincluding an executable portion that uses a third parity strip of the atleast three parity strips at the end of the stripe, wherein the thirdparity strip is a Q parity strip.
 18. The computer program product ofclaim 15, further including an executable portion that rebuilds aselected portion of the stripe having a single disk drive failure andassociated with a first parity strip of the at least three paritystrips.
 19. The computer program product of claim 15, further includingan executable portion that rebuilds the stripe having one or more diskdrive failures and associated with one or more of the two parity stripsaccording to a defined rebuild order.
 20. The computer program productof claim 15, further including an executable portion that: rebuilds a Qparity strip, a data strip or a single parity strip for a single diskfailure upon occurrence of a single disk drive failure; rebuilds the Qparity strip and the data strip or the single parity strip or at leasttwo data strips or parity strips occurring in a similar p-stripeassociated with one or more of the two parity strips upon occurrence ofat least two disk drive failures; or rebuilds the Q parity strip and thedata strip in each section of the stripe associated with the two paritystrips upon occurrence of at least three or more disk drive failures.